Method of producing a ferrule with an optical fiber

ABSTRACT

In a state in which a front end of a single-core fiber is passed through an end surface portion of a reinforcing pipe, an inner surface of the reinforcing pipe and an outer peripheral surface of the single-core fiber are glued together by means of adhesive. By using the same adhesive, an adhesive portion is formed by curing it so as to protrude and taper from the end surface portion of the reinforcing pipe toward the front end of the single-core fiber. Thereafter, a coated optical fiber formed with the adhesive portion is inserted in a ferrule until an end surface portion of the coating of the single-core fiber abuts against the first tapered hole and until the end surface portion of the reinforcing pipe abuts against the second tapered hole. Then, the optical fiber is glued in the ferrule by means of adhesive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority ofJapanese Patent Application No. 2005-159599, filed at the JapanesePatent Office on May 31, 2005, the disclosure of which is incorporatedherein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a ferrule with anoptical fiber.

2. Description of the Related Art

Heretofore, optical connectors have been used as one means for opticallyconnecting optical fibers. Generally, an optical connector is formed bya process in which the front part of a resin coating of a coated opticalfiber is peeled, and then, the thus exposed bare optical fiber isinserted and fixed in an optical-fiber-insertion hole (see e.g.,Japanese Unexamined Patent Application, First Publication No.2000-147320).

FIGS. 5 and 6 are longitudinal cross sectional views illustratingexamples of a conventional ferrule with an optical fiber 110.

Each of these ferrules with an optical fiber 110 is structured such thata bare optical fiber 101 which is exposed at a front end side of acoated optical fiber 103 is inserted in an optical-fiber-insertion hole114 of a ferrule 111 and then fixed by providing adhesive therein. Thecoated optical fiber 103 is formed from the bare optical fiber 101 and aresin coating provided thereupon.

The ferrule 111 is structured such that a capillary 112 made of zirconiaor the like is fixed to a front end side of a ferrule body 113 providedwith a flange 113 a. The capillary 112 is provided with a connection-endface 112 a and an optical-fiber-insertion hole 114 which is in theconnection-end face 112 a and in which the bare optical fiber 101 isinserted and positioned in place. Further, the ferrule body 113 isformed with a coated-fiber-insertion hole 116 in which the coatedoptical fiber 103 is inserted and housed.

In the ferrule 111 of FIG. 5, the coated-fiber-insertion hole 116 isprovided within the range of the ferule body 113, whereas in the ferruleof FIG. 6, the coated-fiber-insertion hole 116 is provided within arange from the ferrule body 113 to a rear end side of the capillary 112.The coated-fiber-insertion hole 116 is larger in diameter than theoptical-fiber-insertion hole 114. A tapered hole 115 is provided betweenthe optical-fiber-insertion hole 114 and the coated-fiber-insertion hole116, which are caused to communicate thereby.

However, in the case in which a front end portion of the coated opticalfiber 103 is inserted and fixed in the ferrule 111 as shown in FIGS. 5and 6, because the difference in shrinkage ratio between the diameter ofthe coated-fiber-insertion hole 116 and the diameter of theoptical-fiber-insertion hole 114 is substantial, then a considerableamount of adhesive Ad inevitably presents in the tapered hole 115. As aresult, because of shrinkage of the adhesive occurring during a curingoperation or due to changes in temperature and because of inclusion ofbubbles in the adhesive, substantial stress acts on the part of theoptical-fiber-insertion hole 114 in the vicinity of the tapered hole115, thereby resulting in deterioration of characteristics of theoptical fiber.

Further, the diameter of the coated optical fiber 103 is, for example,approximately 0.9 mm and thus it is difficult to improve positioningaccuracy of the coated-fiber-insertion hole 116 with respect to an outerperiphery of the coated optical fiber 103. Therefore, there is generallya certain level of clearance (e.g., approximately 0.1 mm or more, as adifference between inside and outside diameters) between the outerperiphery of the coated optical fiber 103 and an inner surface of thecoated-fiber-insertion hole 116. As shown in FIG. 8A, when the opticalfiber is inserted in the ferrule, a center line of the coated opticalfiber 103 is likely to deviate from a center line of thecoated-fiber-insertion hole 116 such that the coated optical fiber bendsor becomes imbalanced due to friction or the like between the resincoating 105 and the inner surface of the coated-fiber-insertion hole116. Alternatively, as shown in FIG. 8B, a front end of the resincoating 105 is likely to abut against the tapered hole 115 in a slanted(biased) manner such that stress locally acts on the resin coating.There is the fear that further deterioration of characteristics of theoptical fiber may result due to damaging bends of the bare optical fiber101. Incidentally, in FIGS. 8A and 8B, the adhesive between the opticalfiber and the inner surface of the hole is not illustrated.

As described above, when the end of the coating of the coated opticalfiber abuts against the inner surface of the tapered hole, or converselywhen a gap which is provided between the end of the coating and theinner surface of the tapered hole is filled with adhesive, there is thefear that external forces may be generated and applied unevenly to thebare optical fiber due to reactive forces from the inner surface of thetapered hole, shrinkage of the adhesive or the like. It is thereforedifficult to produce or assemble a high-performance ferrule with anoptical fiber.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovecircumstances. An object of the invention is to provide a method ofproducing a ferrule with an optical fiber in which it is possible tocontrol worsening of characteristics when the ferrule is secured to afront end of a coated optical fiber.

In order to achieve the above object, according to a first aspect of thepresent invention, there is provided a method of producing a ferrulewith an optical fiber in which a coated optical fiber is fixedly securedto the ferrule, the method comprising:

providing a coated optical fiber, which consists of a single-core fiberincluding a bare optical fiber and a coating and of a reinforcing pipe,wherein, in a state in which a front end of the single-core fiber ispassed through an end surface portion of the reinforcing pipe, anadhesive portion is formed by using at least a first adhesive in such amanner that the adhesive portion protrudes and tapers from the endsurface portion of the reinforcing pipe toward the front end of thesingle-core fiber;

inserting the coated optical fiber in a ferrule provided with a firsttapered hole and a second tapered hole until an end surface portion ofthe coating of the single-core fiber abuts against the first taperedhole and until the end surface portion of the reinforcing pipe abutsagainst the second tapered hole; and

filling a gap between the second tapered hole and the adhesive portionwith a second adhesive.

A second aspect of the present invention is characterized in that, inthe first aspect of the present invention, the first adhesive and thesecond adhesive are substantially the same.

A third aspect of the present invention is characterized in that, in thefirst aspect of the present invention, the first adhesive and the secondadhesive are different from one another.

A fourth aspect of the present invention is characterized in that, inthe first aspect of the present invention, the ferrule consists of aferrule body and a capillary fixedly secured to the ferrule body.

A fifth aspect of the present invention is characterized in that, in thefourth aspect of the present invention, the ferrule body is providedwith a coated-fiber-insertion hole in which the reinforcing pipe isreceived.

A sixth aspect of the present invention is characterized in that, in thefifth aspect of the present invention, the capillary has aconnection-end face at a side opposite to a side where the capillary isfixedly secured.

A seventh aspect of the present invention is characterized in that, inthe sixth aspect of the present invention, the capillary has anoptical-fiber-insertion hole which is in the connection-end face and inwhich the bare optical fiber is inserted.

A eighth aspect of the present invention is characterized in that, inthe seventh aspect of the present invention, the capillary has asingle-core-fiber-insertion hole which communicates with theoptical-fiber-insertion hole and which is in the side where thecapillary is fixedly secured, and wherein the coating of the single-corefiber is received in the single-core-fiber-insertion hole.

A ninth aspect of the present invention is characterized in that, in theeighth aspect of the present invention, the first tapered hole is formedat a boundary between the optical-fiber-insertion hole and thesingle-core-fiber-insertion hole.

A tenth aspect of the present invention is characterized in that, in theninth aspect of the present invention, the second tapered hole is formedat a boundary between the single-core-fiber-insertion hole and thecoated-fiber-insertion hole.

In the present invention, the adhesive portion having a tapered-shape isprovided on the end of the reinforcing pipe and around the single-corefiber such that, when the end of the reinforcing pipe of the coatedoptical fiber abuts against the second tapered hole, the adhesiveportion is received between the end of the reinforcing pipe and theinner surface of the second tapered hole to thereby reduce the amount ofadhesive present in the second tapered hole. As a result, internalstress generated in the adhesive can be lessened and adverse effects onthe optical fiber can be further reduced.

In addition, by applying or pressing the end of the reinforcing pipetoward the second tapered hole, it is possible to securely maintain agap between a surface of the adhesive and the inner surface of thesecond tapered hole, and therefore, when the ferrule and the coatedoptical fiber are glued together, the flow of adhesive is not inhibited.

Incidentally, to form an adhesive portion, it is necessary to expose afront portion of the single-core fiber by protruding it from the end ofthe reinforcing pipe. In the present invention, in order to securestable positioning of the single-core fiber, the end of the primarycoating is caused to abut against the first tapered hole and at the sametime the end of the reinforcing pipe is caused to abut against thesecond tapered hole. With this provision, a center line of thesingle-core fiber does not substantially deviate from a center line ofthe single-core-fiber-insertion hole, and therefore, it is possible toposition and fix the single-core fiber while maintaining it in astraight state between the first tapered hole and the second taperedhole and then to control adverse effects on the bare optical fiber inthe optical-fiber-insertion hole. Further, a film thickness of anadhesive provided in a gap between the inner surface of thesingle-core-fiber-insertion hole and the outer surface of thesingle-core fiber is ideally equalized, and therefore, even when cureand shrinkage of the adhesive occurs due to changes in temperature, itis possible to eliminate factors which have adverse consequences tooptical transmission, such as internal stress and bending deformation ofthe optical fiber in the single-core fiber and of the bare optical fiberin the optical-fiber-insertion hole, and to securely and properlymaintain optical properties.

The above and other aspects of the present invention will becomeapparent upon consideration of the following detailed description ofexemplary embodiments thereof, particularly when taken in conjunctionwith the accompanying drawings wherein like reference numerals in thevarious figures are utilized to designate like components.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the invention will be made more apparentby describing in detail exemplary embodiments thereof with reference tothe attached drawings in which:

FIGS. 1A and 1B are explanatory views for explaining a method ofproducing a ferrule with an optical fiber according to the presentinvention, wherein FIG. 1A is a fragmentary view illustrating a mainportion of a coated optical fiber in which an adhesive portion is formedby means of adhesive cured on an end of a reinforcing pipe, and whereinFIG. 1B is a view illustrating an appearance of a bare optical fiberinserted as shown in FIG. 1A.

FIG. 2 is a longitudinal sectional view illustrating a main portion ofthe ferrule with the optical fiber.

FIGS. 3A and 3B are views illustrating a first practical example of theferrule with the optical fiber, wherein FIG. 3A is a longitudinal crosssectional view illustrating the ferrule with the optical fiber andwherein FIG. 3B is a longitudinal cross sectional view illustrating theferrule only.

FIGS. 4A and 4B are views illustrating a second practical example of theferrule with the optical fiber, wherein FIG. 4A is a longitudinal crosssectional view illustrating the ferrule with the optical fiber andwherein FIG. 4B is a longitudinal cross sectional view illustrating theferrule only.

FIG. 5 is a longitudinal cross sectional view illustrating a firstexample of a conventional ferrule with an optical fiber.

FIG. 6 is a longitudinal cross sectional view illustrating a secondexample of a conventional ferrule with an optical fiber.

FIG. 7 is a longitudinal cross sectional view for explaining theinfluence of shrinkage of adhesive in the vicinity of a tapered hole ofa conventional ferrule with an optical fiber.

FIGS. 8A and 8B are partially longitudinal cross sectional views forexplaining problems which arise during the insertion of an optical fiberin a conventional ferrule, wherein FIG. 8A is a view illustrating anappearance of an optical fiber inserted and wherein FIG. 8B is a viewillustrating an appearance of an optical fiber bent due to abutting ofan end of a resin coating of the optical fiber against a tapered hole.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

With reference to the attached figures, exemplary embodiments of thepresent invention will now be described below. The described exemplaryembodiments are intended to assist the understanding of the invention,and are not intended to limit the scope of the invention in any way.

FIGS. 1A and 1B are views for explaining a method of producing a ferrulewith an optical fiber according to the present invention. FIG. 1A is afragmentary view showing a main portion of a coated optical fiber inwhich an adhesive portion is previously formed on an end of areinforcing pipe by means of adhesive being cured. FIG. 1B is alongitudinal sectional view showing an appearance of the ferrule intowhich the coated optical fiber shown in FIG. 1A is inserted. FIG. 2 is alongitudinal sectional view showing a main portion of the ferrule withthe optical fiber. Incidentally, in FIG. 1B, the adhesive portion forbonding an inner surface of a hole of the ferrule and a coated opticalfiber is not illustrated.

Ferrules with optical fibers which are produced in accordance with thepresent invention may include a ferrule with an optical fiber such as aferrule with an optical fiber 10 in which the ferrule 11 is mounted on aleading end of the coated optical fiber 3 as show in FIGS. 3A and 4A.

As show in FIG. 1A, the coated optical fiber 3 of the present inventionis provided with a single-core fiber 2 composed of a bare optical fiber1 and of a primary coating 4 that covers an outer circumference of thebare optical fiber 1 and with a reinforcing pipe 5 which is fitted on anouter periphery of the single-core fiber 2. The type of optical fiber isnot limited to this. Various types of optical fibers such as forexample, a silica-based single-mode optical fiber, apolarization-maintaining optical fiber (PANDA fiber etc.) in whichstress-applying parts are provided within a cladding at opposing sideswith respect to a core, a fiber with deformation applied, and the likecan be employed. The diameter of the bare optical fiber 1 may be about125 μm or about 80 μm. However, it is not limited as such. Anultraviolet curable resin or the like can be employed as a resin forforming the primary coating 4. Further, a polyamide resin, a polyesterresin, etc. can be employed as a resin for forming the reinforcing pipe5.

As shown in FIGS. 3B and 4B, the ferrule 11 is a combination of aferrule body 13 provided with outwardly protruding flanges 13 a formedone at each side thereof and of a generally-cylindrical shaped capillary12 which is fixedly secured to a front end side of the ferrule body 13.In the ferrule body 13A is formed a coated-fiber-insertion hole 16 intowhich the coated optical fiber 3 is inserted or received. The ferrulebody 13 can be formed of zirconia (Zr), stainless steel (SUS), syntheticresin, or the like.

The capillary 12 is provided with a connection-end face 12 a which isformed at a front end side of the ferrule 11, with anoptical-fiber-insertion hole 14 which is in the connection-end face andinto which a bare optical fiber 1 is inserted and held in place, andwith a single-core-fiber-insertion hole 15 which communicates with theoptical-fiber-insertion hole 14 at a rear end side opposed to theconnection-end face 12 a of the optical-fiber-insertion hole 14 and intowhich a single-core fiber 2 is inserted and held in place.

The capillary 12 can be formed of ceramic such as, e.g., zirconia (Zr),or of glass such as amorphous glass, crystallized glass or the like. Theexternal diameter of the capillary 12 can be about 2.5 mm applicable toa SC (Single Fiber Coupling) type optical connector recommended in JIS C5973 etc. or about 1.25 mm applicable to a MU (Miniature-Unit) typeoptical connector recommended in JIS C 5983, etc. There are nolimitations on the diameter thereof. It is preferable that thedifference between an inner diameter of the optical-fiber-insertion hole14 and an outer diameter of the bare optical fiber 1 be made small(e.g., about 0.001 mm) to such an extent that easy positioning of thebare optical fiber 1 can be assured.

As shown in FIG. 2, an end portion 4 a of the primary coating 4 of thesingle-core fiber 2 abuts a first tapered hole 17 which is disposedbetween the optical-fiber-insertion hole 14 and thesingle-core-fiber-insertion hole 15. Because the end portion 4 a of theprimary coating 4 abuts an inner surface of the first tapered hole 17,the amount (or volume) of adhesive Ad present in a gap between the endportion 4 a of the primary coating 4 and the inner surface of the firsttapered hole 17 is reduced, thus lessening internal stress within theadhesive. As a result, adverse effects on the optical fiber can furtherbe reduced. The taper angle θ1 of the inner surface of the first taperedhole 17 is preferably in the range of 30 degrees to 165 degrees. As atypical example, it is around 90 degrees. The larger the taper angle,the more the fiber positioning through abutment is eased and the amount(or volume) of adhesive Ad present within the first tapered hole 17 isreduced. Thus, internal stress within the adhesive is lessened. As aresult, fortunately, adverse effects on the optical fiber caneffectively be reduced. In the case where the taper angle θ1 is lessthan 30 degrees, there is a possibility of causing problems in that theoptical fiber tends to bend along the inner (tapered) surface when theend portion 4 a of the primary coating 4 abuts the inner surface of thefirst tapered hole 17, and in that the amount of the adhesive becomeslarge, thus resulting in more adversely effects due to greatercontraction of the adhesive. As such, this is not preferable.

As shown in FIG. 2, an end portion 5 a of the reinforcing pipe abuts asecond tapered hole 18 which is disposed between thesingle-core-fiber-insertion hole 15 and the coated-fiber-insertion hole16. Because the end portion 5 a of the reinforcing pipe 5 abuts an innersurface of the second tapered hole 18, the amount (or volume) ofadhesive Ad present in a gap between the end portion 5 a of thereinforcing pipe 5 and the inner surface of the second tapered hole 18is reduced, thus lessening internal stress within the adhesive. As aresult, adverse effects on the optical fiber can further be reduced.

The taper angle θ2 of the inner surface of the first tapered hole 17 ispreferably in the range of 60 degrees to 90 degrees. As a typicalexample, it is around 60 degrees.

As to the ratio between the length of the optical-fiber-insertion hole14 formed in the capillary 12 and the length of thesingle-core-fiber-insertion hole 15 formed in the capillary 12, variousvalues thereof are permissible. Namely, various configurations, such asone where the length L1 of the optical-fiber-insertion hole 14 is longerthan the length L2 of the single-core-fiber-insertion hole 15 as shownin FIGS. 3A and 3B, another one where the length L2 of thesingle-core-fiber-insertion hole 15 is longer than the length L1 of theoptical-fiber-insertion hole 14 as shown in FIGS. 4A and 4B, and afurther one where, although not shown in a figure, the length L2 of thesingle-core-fiber-insertion hole 15 is nearly equal to the length L1 ofthe optical-fiber-insertion hole 14, are acceptable.

The difference between the inside diameter of thesingle-core-fiber-insertion hole 15 and the outside diameter of thesingle-core fiber 2 (or of the primary coating 4) is preferablyapproximately 0.1 mm. Therefore, for example, if the outside diameter ofthe single-core fiber 2 is 0.4 mm, the inside diameter of thesingle-core-fiber-insertion hole 15 is set to be around 0.5 mm. In acase where the difference between the inside diameter of thesingle-core-fiber-insertion hole 15 and the outside diameter of thesingle-core fiber 2 is large, it is possible to compensate for such adiameter difference by means of a non-illustrated protective tube madeof synthetic resin, elastomer or the like, to be fitted on the primarycoating 4. As can be seen from the foregoing, in the present invention,a single-core fiber simply represents an optical one which has anoutside diameter between a bare optical fiber and a coated opticalfiber. It may represent a single-core fiber in which a primary coatingis provided on a bare optical fiber, in the real sense of the term. Inaddition thereto, it may represent a single-core fiber where aprotective tube or the like is fitted on a primary coating. From thestandpoint of easy positioning, the length L2 of the single-core-fiberinsertion hole 15 is preferably 2 mm or more, and more preferably, in arange from 2 mm to 5 mm.

The difference between the inside diameter of the coated-fiber-insertionhole 16 and the outside diameter of the coated optical fiber 3 ispreferably approximately 0.1 mm. Therefore, if the outside diameter ofthe coated optical fiber 3 (of the reinforcing pipe 5) is approximately0.9 mm, it is preferable that the inside diameter of thecoated-fiber-insertion hole 16 be set to around 1.0 mm. Therefore, acenterline of the coated optical fiber 3 is not easily shifted relativeto a centerline of the coated-fiber-insertion hole 16. It is thuspossible to limit bending, centerline deviation of the coated opticalfiber 3, and the like.

As shown in FIG. 1A, an inner surface of the reinforcing pipe 5 is gluedto an outer peripheral surface of the single-core fiber 2 by adhesive.If diameter of the optical fiber is within a range from 0.17 mm to 20mm, the inside diameter of the reinforcing pipe 5 is approximately 0.21mm (the outside diameter of the reinforcing pipe 5 is for example 0.9mm). With this structure, when inserting an optical fiber or whenexternal forces such as vibrations are exerted on the optical fiber, itis possible to limit bending of and internal pressure upon thesingle-core fiber 2 within the reinforcing pipe 5.

The adhesive by which the inner surface of the reinforcing pipe 5 isglued to the outer peripheral surface of the single-core fiber 2 formsan adhesive portion 6 which protrudes and tapers from an end surfaceportion 5 a of the reinforcing pipe 5 toward a front end side of thesingle-core fiber 2. This adhesive portion 6 leaves exposed (uncovers) aperipheral edge region (or ring region) 5 b of the end surface portion 5a of the reinforcing pipe 5 and has a tapered shape so as to protrudetoward the front end side of the single-core fiber 2.

Next, with reference to FIGS. 1A, 1B, and 2, a producing method of theferrule with the optical fiber 10 according to the present inventionwill be explained.

Firstly, the single-core fiber 2 is inserted in the reinforcing pipe 5which has previously been cut to a predetermined length. Then, by meansof adhesive, the inner surface of the reinforcing pipe 5 and the outerperipheral surface of the single-core fiber 2 are glued. Thereat, asshown in FIG. 1A, a leading end portion of the single-core fiber 2 isexposed from an end portion of the reinforcing pipe 5, and then, theadhesive portion 6 is cured and formed so as to protrude and taper fromthe end surface portion 5 a of the reinforcing pipe 5 toward the frontend side of the single-core fiber 2. The adhesive portion 6 cured andformed in a tapered shape preferably has a taper angle which is nearlyequal to the taper angle θ2 of the second tapered hole 18. The adhesiveportion 6 may be smaller in size than the second tapered hole 18. Thereis no need for both of them to be made in the same shape.

Next, the primary coating 4 is stripped off from a front end portion ofthe single-core fiber 2 such that a portion of the bare optical fiber 1is exposed. The length between the exposed portion of the bare opticalfiber 1 and the end surface portion 5 a of the reinforcing pipe 5, i.e.,the length of an exposed portion of the primary coating 4 of thesingle-core fiber 2 is set to be nearly equal to the length L2 of thesingle-core-fiber-insertion hole 15. This can easily be done bycontrolling a position of an area of the primary coating to be strippedoff.

Incidentally, another procedure is adoptable in which the primarycoating 4 is stripped off from the front end portion of the single-corefiber 2 such that a portion of the bare optical fiber 1 is exposed, andthereafter, the single-core fiber 2 is inserted in the reinforcing pipe5. In this case, by shifting along the single-core fiber 2 a position ofthe reinforcing pipe 5 with respect to the end surface portion 4 a ofthe primary coating 4, it is possible to control an exposure length ofthe primary coating 4.

The length of the portion of the bare optical fiber 1 exposed is set tobe nearly equal to or greater than the length L1 of theoptical-fiber-insertion hole 14. In the case in which the bare opticalfiber 1 portion is long so that the front end thereof protrudes from theoptical-fiber-insertion hole 14, control of appropriate positioning ofan end surface of the bare optical fiber 1 with respect to theconnection-end face 12 a can be done by cutting, polishing and the likesubsequent to an assembly operation. Therefore, when stripping off theprimary coating 4, the bare optical fiber 1 can be exposed so that thelength thereof is sufficiently longer than the length of theoptical-fiber-insertion hole 14.

Further, as shown in FIG. 1B, the coated optical fiber 3 with theadhesive portion 6, which has been previously cured in the tapered shapeas described above, is inserted in the ferrule 11 such that the endsurface portion 4 a of the primary coating 4 of the single-core fiber 2abuts against the first tapered hole 17 and, at the same time, the endsurface portion 5 a of the reinforcing pipe 5 abuts against the secondtapered hole 18. Finally, the bare optical fiber 1 is housed in theoptical-fiber-insertion hole 14 and the single-core fiber 2 is housed inthe single-core-fiber-insertion hole 15.

As described above, in the present embodiment, in order to form theadhesive portion 6, the exposed portion of the primary coating 4 isprovided between the bare optical fiber 1 and the coated optical fiber3. The end surface portion 4 a of the primary coating 4 and the endsurface portion 5 a of the reinforcing pipe 5 abut against the first andsecond tapered holes 17, 18, respectively. Therefore, the exposedportion of the single-core fiber 2 (or of the primary coating 4) can bekept straight due to abutting forces against the first and the secondtapered hole 17, 18. Namely, because the portions against which the endsurface portions 4 a and 5 a abut have been made to be tapered holes,the end surface portions 4 a and 5 a receive at circumferences thereofpressing forces, which are caused by reaction from inner surfaces of thetapered holes and which are radially inwardly directed.

Then, as shown in FIG. 2, peripheral edges 4 b and 5 b of the endsurface portion 4 a of the primary coating 4 and of the end surfaceportion 5 a of the reinforcing pipe 5 are deformed inwards. In otherwords, the reinforcing pipe can further advance from a position in whichthe end surface portions 4 a and 5 a firstly touch inner surfaces of thetapered hole 17 and 18 to a deeper position (a connection-end face side,i.e., left hand side in FIG. 2). Further, when the peripheral edges 4 band 5 b of the end surface portions 4 a and 5 a have been inwardlydeformed or squeezed, the peripheral edges 4 b and 5 b of the endsurface portions 4 a and Sa closely touch the inner surfaces of thetapered holes 17 and 18 due to the elastic force of the synthetic resinmaterial which forms the primary coating 4 and the reinforcing pipe 5.The single-core fiber 2 can be supported in a radially equalized mannersuch that a center axis of the single-core fiber 2 coincides with acenter axis of the single-core-fiber-insertion hole 15. Furthermore,because both of the first tapered hole 17 and the second tapered hole 18are formed in the capillary 12, even if there is a positional deviationbetween the capillary 12 and the ferrule body 13, the positionalrelationship between the first and the second tapered holes 17, 18 ismaintained unchanged, and therefore, such positional deviation cannotadversely affect the positioning of the single-core fiber 2.

As described above, the center axis of the single-core fiber 2 does notdeviate from the center axis of the single-core-fiber-insertion hole 15,and therefore, it is possible to secure the single-core fiber 2 in placebetween the first tapered hole 17 and the second tapered hole 18 whilemaintaining the single-core fiber 2 in a straight line. As a result,adverse effects with respect to the bare optical fiber 1 in theoptical-fiber-insertion hole 14 can effectively be eliminated. Further,the single-core-fiber-insertion hole 15 is provided between theoptical-fiber-insertion hole 14 and the coated-fiber-insertion hole 16such that they are substantially separated. With this structure,deflections of the coated optical fiber 3 and the reinforcing pipe 5 andstress induced therein have little adverse effect on the bare opticalfiber 1 in coated-fiber-insertion hole 16. Furthermore, a thickness ofan adhesive in a cylindrical gap between an inner surface of thesingle-core-fiber-insertion hole 15 and an outer surface of thesingle-core fiber 2 is circumferentially equalized. Therefore, even whencure and shrinkage of the adhesive occurs due to changes in temperature,it is possible to eliminate factors which have adverse consequences tooptical transmission, such as internal stress and bending deformation ofthe optical fiber in the single-core fiber 2 and of the bare opticalfiber 1 in the optical-fiber-insertion hole 14, and to securely andproperly maintain optical properties.

As shown in FIG. 2, the optical fiber is secured in the ferrule 11 bymeans of the adhesive Ad. The adhesive Ad for bonding the optical fiberwith the ferrule can be applied on a periphery of the optical fiberprior to inserting the optical fiber in the ferrule. Another operationis possible in which the adhesive is first applied or provided in theferrule, and thereafter, the optical fiber is inserted therein.

In accordance with the present invention, the adhesive by which thesingle-core fiber 2 and the reinforcing pipe 5 are glued together formsthe adhesive portion 6 which is cured so as to protrude and taper fromthe end surface portion 5 a of the reinforcing pipe 5 toward the frontend side of the single-core fiber 2. The end surface portion 5 a ismoved to abut against the second tapered hole 18 such that a volume of aspace enclosed with the inner surface of the second tapered hole 18,with the end surface portion 5 a of the reinforcing pipe 5, and with theadhesive portion 6 is reduced in such a manner that the adhesive portion6 displaces part of the adhesive Ad present in this enclosed space. As aresult, a volume of the adhesive Ad filled in this space can be madesmall. Therefore, even when curing and shrinkage of the adhesive Ad inthe enclosed space occurs due to changes in temperature, internal stressinduced in the adhesive can be reduced, and therefore, adverseconsequences to the optical fiber can be prevented. The adhesive portion6 can be easily and simply formed around the primary coating 4. Theadhesive portion 6 formed in a protruding manner does not involve anyadverse effects on the bare optical fiber 1. Further, it is easy tocontrol the shape of the adhesive portion 6 before or after the adhesiveis cured.

Moreover, by simply pressing the peripheral edge region 5 b of the endsurface portion 5 a of the reinforcing pipe 5 against the inner surfaceof the second tapered hole 18, a predetermined gap can be securelyformed between the outer surface of the adhesive portion 6 and the innersurface of the second tapered hole 18. Therefore, when the ferrule 11and the coated optical fiber 3 are glued together, the flow of adhesiveAd is not inhibited.

Still further, the end surface portion 4 a of the primary coating 4 ismoved to abut against the inner surface of the first tapered hole 17such that an amount (volume) of the adhesive Ad in the first taperedhole 17 is reduced. Therefore, internal stresses induced in the adhesivecan be reduced. As a result, adverse effects on the optical fiber can befurther limited.

In addition, the second tapered hole 18 is separated in a lengthwisedirection of the optical fiber, from the bare optical fiber 1 insertedin the optical-fiber-insertion hole 14. The single-core fiber 2 can bepositioned and fixed by means of the single-core-fiber-insertion hole 15which is provided between the optical-fiber-insertion hole 14 and thecoated-fiber-insertion hole 16. Therefore, bending deformation of thecoated optical fiber 3 and internal stress in the reinforcing pipe 5 donot substantially affect the bare optical fiber 1 received in theoptical-fiber-insertion hole 14.

As compared with the conventional examples shown in FIGS. 5 and 6, inthe present invention, the single-core-fiber-insertion hole 15 isprovided between the optical-fiber-insertion hole 14 and thecoated-fiber-insertion hole 16, and has a diameter intermediate betweenthe diameters of the holes 14 and 16. As compared to the shrinkage ratioof the tapered hole 115 of the above conventional examples, theshrinkage ratio of the first tapered hole 17 positioned between theoptical-fiber-insertion hole 14 and the single-core-fiber-insertion hole15 is small. As a result, stress is not concentrated at the end of thesingle-core fiber 2 (the exposed portion side of the bare optical fiber1). Adverse effects exerted by bubbles and shrinkage of the adhesive arealso small. Deterioration of characteristics can be reduced. A highperformance ferrule with the fiber can be produced or assembled.

As a single-core fiber (2), a silica-based optical fiber is used, inwhich the outer diameter (cladding diameter) of the bare optical fiber(1) is about 0.125 mm and the outer diameter of the primary coating (4)is about 0.25 mm. A reinforcing pipe (5) whose inner diameter is 0.4 mmor so and whose outer diameter is 0.9 mm or so is fitted on thesingle-core fiber(2) and fixed thereto by an adhesive to thereby form acoated optical fiber (3). At this time, part of the adhesive is made toprotrude from the end surface portion 5 a of the reinforcing pipe 5toward the front end side of the single-core fiber 2 and thereaftercured so as to form a tapered adhesive portion 6 around the single-corefiber 2 (see FIG. 1A).

In this embodiment, a ferrule 11 is used which has specifications inwhich the taper angle θ1 of the first tapered hole 17 is approximately90°, the taper angle θ2 of the second tapered hole 18 is approximately60°, the inner diameter of the optical-fiber-insertion hole 14 isapproximately 0.126 mm, the inner diameter of thesingle-core-fiber-insertion hole 15 is approximately 0.3 mm, and theinner diameter of the coated-fiber-insertion hole 16 is approximately1.0 mm. As such, the gap between the primary coating 4 and thesingle-core-fiber-insertion hole 15 (i.e., the difference between theinner diameter and the outer diameter) is approximately 0.1 mm and thegap between the reinforcing pipe 5 and the coated-fiber-insertion hole16 (i.e., the difference between the inner diameter and the outerdiameter) is approximately 0.1 mm.

The adhesive portion 6 formed of the adhesive by which the single-corefiber 2 and the reinforcing pipe 5 are glued together is provided on thecoated optical fiber 3 (the reinforcing pipe 5). The coated opticalfiber 3 is applied with uncured adhesive, and thereafter, it is insertedin the above-mentioned ferrule 11 until the end surface portion 4 a ofthe primary coating 4 abuts against the first tapered hole 17 and untilthe end surface portion 5 a of the reinforcing pipe 5 abuts against thesecond tapered hole 18. Then, the adhesive Ad for gluing the coatedoptical fiber 3 and the ferrule 11 is cured such that a ferrule with anoptical fiber 10 is formed and produced.

In connection with the thus produced ferrule with the optical fiber 10,the extinction ratio was measured. The extinction ratio has beenimproved to such an extent that it reaches to the level of 35 to 42 dB.In contrast, as shown in FIGS. 5 and 6, in an evaluation of a ferrulewith an optical fiber 110 structured by a ferrule in which anoptical-fiber-insertion hole 114 and a coated-fiber-insertion hole 116are caused to communicate with one another via a tapered hole 115 only,the extinction ratio reaches only to the level of 25 dB. In accordancewith the present invention, it is possible to remove adverse affectsexerted by shrinkage of the adhesive, bubbles in the adhesive and thelike, and to control worsening of optical properties.

Incidentally, the adhesive for forming an adhesive portion 6 and theadhesive for fixedly securing the coated optical fiber may be the sameor different.

The present invention is applicable to optical connection of opticalfibers in various fields such as optical communications and opticalmeasurement using optical fibers.

While the invention has been specifically shown and described withreference to exemplary embodiments thereof, the invention is not to beconsidered as being limited by the foregoing description. It is apparentthat various changes in form and details may be made by those ofordinary skill in the art while referring to the present specification.Therefore, such modifications can be made without departing from thespirit and scope of the invention as defined by the following claims.

1. A method of producing a ferrule with an optical fiber in which acoated optical fiber is fixedly secured to the ferrule, the methodcomprising: providing a coated optical fiber, which consists of asingle-core fiber including a bare optical fiber and a coating and of areinforcing pipe, wherein, in a state in which a front end of thesingle-core fiber is passed through an end surface portion of thereinforcing pipe, an adhesive portion is formed by using at least afirst adhesive in such a manner that the adhesive portion protrudes andtapers from the end surface portion of the reinforcing pipe toward thefront end of the single-core fiber; inserting the coated optical fiberin a ferrule provided with a first tapered hole and a second taperedhole until an end surface portion of the coating of the single-corefiber abuts against the first tapered hole and until the end surfaceportion of the reinforcing pipe abuts against the second tapered hole;and filling a gap between the second tapered hole and the adhesiveportion with a second adhesive.
 2. The method according to claim 1,wherein the first adhesive and the second adhesive are substantially thesame.
 3. The method according to claim 1, wherein the first adhesive andthe second adhesive are different from one another.
 4. The methodaccording to claim 1, wherein the ferrule consists of a ferrule body anda capillary fixedly secured to the ferrule body.
 5. The method accordingto claim 4, wherein the ferrule body is provided with acoated-fiber-insertion hole in which the reinforcing pipe is received.6. The method according to claim 5, wherein the capillary has aconnection-end face at a side opposite to a side where the capillary isfixedly secured.
 7. The method according to claim 6, wherein thecapillary has an optical-fiber-insertion hole which is in theconnection-end face and in which the bare optical fiber is inserted. 8.The method according to claim 7, wherein the capillary has asingle-core-fiber-insertion hole which communicates with theoptical-fiber-insertion hole and which is in the side where thecapillary is fixedly secured, and wherein the coating of the single-corefiber is received in the single-core-fiber-insertion hole.
 9. The methodaccording to claim 8, wherein the first tapered hole is formed at aboundary between the optical-fiber-insertion hole and thesingle-core-fiber-insertion hole.
 10. The method according to claim 9,wherein the second tapered hole is formed at a boundary between thesingle-core-fiber-insertion hole and the coated-fiber-insertion hole.